1. Field of the Invention
The present invention relates generally to automotive collision avoidance, and mitigation or attenuation, and more specifically to avoiding or mitigating vehicle collisions between cargo carried as a projecting load and any other vehicle.
2. Prior Art
The basis of providing vehicle bumpers is to provide a durable collision interface with relatively large surface area to transmit the collision force to the vehicle chassis regardless of the point of impact or the distribution of collision forces. Once transmitted to the chassis, the impact forces are transmitted to the vehicle occupants via safety belts and/or air bags. This widely employed method works to lessen the effects of highly concentrated impacts, such as those with trees or support columns.
There exists, however, a common and necessary highway transport practice which, if involved in a collision, never allows for any current automobile safety system to mitigate the impact.
In transporting long non-separable loads, such as utility poles, on commercial motor vehicles, it is common practice to secure the majority of the load to the truck or trailer, and allow a significant portion of the load to project rearward beyond the extent of the truck or trailer frame. This practice may result from the need to transport loads, sometimes exceeding 100′ in length, on roads and highways while maintaining a relatively short vehicle wheelbase for maneuverability. Alternately, a motor carrier may have to, on occasion, transport a load which is not exceptionally long in absolute terms, but is longer than the equipment can accommodate without projection. In either case, the projected load presents a grave danger to other vehicles, especially automobiles, because of two intrinsic geometric parameters of the projecting load.
First, the nature of heavy truck and trailer design and manufacture yields cargo carrying decks which are 3.0′-5.0′ above grade level. This height directly corresponds to the elevation above the front/hood area and below the roof of most passenger vehicles (i.e., the height of a vehicle windshield). If a passenger vehicle collides with a projecting load, the end of the projecting load will pierce the windshield of the automobile, exposing the occupants to extraordinary risk of severe injury or death.
Second, projecting loads generally exhibit a high slenderness ratio i.e. the longitudinal dimension is much, much larger than the cross-sectional dimensions. For example: a truck/trailer combination carrying a projecting size #1 utility pole will typically be only 1.0′ in diameter. This slenderness has two consequent effects: First, in combination with the load height above grade, the driver of a vehicle behind the projecting load is viewing only the cross section of the load. This means that the following driver has only a small area of focusing surface on which to judge his proximity to the projecting load (0.78 ft2 in the case of the #1 utility pole). This can easily lead to the eyes of the following driver focusing on the much larger surface area of the rear truck or trailer frame, which would underestimate the proximity by the projection distance, which is commonly 8.0′-12.0′ and often more as regulations stipulate no maximum projection. In addition to misjudgment of proximity, in the event of a collision with a projecting load the typical slenderness of projecting loads concentrates the impact force on a small area. This, combined with the typical mass, rigidity, and secure attachment of projected loads (utility poles, bridge trusses, I-beams, etc) when compared to the strength of the upper portion of a passenger vehicle, results in the immediate deformation and failure of the passenger vehicle components (windshield, roof, etc.) and exposure of the passengers to the risk of severe injury or death in any collision of appreciable magnitude.
In addition to bumpers, safety belts, and other systems simply transmitting impact forces to vehicle occupants, highway safety advancements such as air bags, crumple zones, and inertia-absorbing highway barriers, have made great strides in reducing casualties resulting from automobile collisions by attenuating the forces resulting from collisions of all magnitudes. The basic principle on which all these systems operate is as follows: the net kinetic energy of the impact is dissipated or absorbed by deformation of some mitigation material or structure. This process lowers the peak transmitted forces while lengthening the time over which any unabsorbed forces are transmitted. Based on the well-documented success of such devices, any collision barrier or bumper will benefit from the addition of an additional mitigation system.